The goals of the proposed work are to determine the properties of central visual mechanisms sensitive to colored patterns and to place this knowledge in the context of natural viewing situations, in which the visual system is exposed to lights reflected from surfaces. An account of color constancy that I have developed in preliminary work stresses that changing the illumination of surfaces can help a visual system determine surface color properties and so construct a more stable visual world. The sensitivity to changing color signals suggested by the theory requires mechanisms of color vision with receptive fields that are inseparable in their chromatic and their spatiotemporal properties. I propose to measure and model these in three psychophysical projects that concern the appearance, detectability and discriminability of color patterns displayed on a television monitor. The first project will measure the appearance of time-varying color patterns in an investigation of simultaneous color contrast and color contrast gain control. The aims are to reveal mechanisms through which the color of a surface is influenced by those of surrounding surfaces, and to determine the spatiochromatic organization and sensitivities of these mechanisms. The second project will measure the foveal detectability of colored patterns through a series of noise-masking experiments. The aims are to determine the organization of color pattern detection mechanisms under conditions of focused attention and to compare human performance to an ideal observer model of color pattern detection. The third project will examine the detection of static and changing colored patterns using visual search and texture discrimination paradigms. The aims are to determine the visual field distribution of detection mechanisms with spatiochromatically-inseparable receptive fields and to link more tightly color constancy phenomena to human performance through an examination of what kind of changes in color displays are readily detected.